Femtosecond pulse shaping has found widespread use for many scientific and industrial applications since its inception nearly 20 years ago. The development of a commercial apparatus for computer-controlled, high-fidelity phase and amplitude pulse shaping has greatly facilitated the application of pulse shaping methods to diverse problems such as optical characterization of materials, time-division multiplexing in signaling systems, laser microscopy, and optical control of matter. Transformation of a single input optical pulse into one or more output pulses by manipulating the spectral properties of the input pulse in controlled fashion is widely achieved through the use of a liquid crystal spatial light modulator array of the type manufactured by, for example, Cambridge Research & Instrumentation (Woburn, Mass.). Such a device includes two one-dimensional liquid crystal spatial light modulators, each oriented in a plane transverse to the light propagation direction. The modulators are transmissive for optical wavelengths in the range 400-1600 nm, and can be refreshed at a rate of roughly 10-100 ms, affording the operator a means of adjusting either the phase or, in combination with additional optics, the amplitude of an input pulse with each one-dimensional spatial light modulator. In order to shape both the amplitude and phase of an optical waveform, both one-dimensional spatial light modulators must be aligned and operated in tandem.
Spatial light modulator (SLM) arrays comprise discrete, addressable pixel elements. The waveforms produced following standard phase and/or amplitude shaping in such arrays often contain replicas due to finite sampling effects. In addition, the utility of a pulse shaper based on a spatial light modulator array is only fully exploited if each pixel element of the SLM is capable of contributing a full 2π phase retardation at the wavelength of the light which impinges upon it.
Techniques for shaping optical waveforms are disclosed in the following patents: U.S. Pat. No. 5,719,650 entitled “HIGH FIDELITY SPATIAL LIGHT MODULATOR” and U.S. Pat. No. 5,682,262 entitled “METHOD AND DEVICE FOR GENERATING SPATIALLY AND TEMPORALLY SHAPED OPTICAL WAVEFORMS,” the contents of which are incorporated by reference herein.